More than any other part of a building, its roof system components must complement each other. From the deck to the insulation to the membrane, careful selection and installation of all roofing materials are necessary for a high-performance roof assembly.
Insulation is a crucial component, of course, because it contributes to a roof system's thermal performance and overall durability while providing a substrate for the roof membrane. And the decision of which insulation type to use can profoundly affect your profitability.
Expanded polystyrene (EPS) rigid foam insulation is one insulation type that should be considered. Although you probably are familiar with EPS, you might not be aware of the wide range of products available and the ways EPS can help reduce labor and material costs.
EPS in short
EPS is a closed-cell, rigid foam insulation that is recyclable. EPS insulation is provided in conventional flat stock, pre-cut tapered panels, and specialty panels that incorporate factory-laminated facers or cover boards.
You can use EPS insulation within fully adhered, ballasted and mechanically fastened assemblies. When appropriately configured as part of a roof assembly, EPS may be used with many roof membrane types, such as TPO, PVC and EPDM, as well as built-up roof (BUR) and polymer-modified bitumen systems.
EPS is lightweight and easy to handle and comes in compressive resistance values from 10 to 60 pounds per square inch, making it suitable for virtually any loads typically encountered on roofs. The material has excellent moisture resistance, is dimensionally stable and retains its R-value during the long term.
Unlike other types of rigid foam insulation that might lose up to 20 percent of their initial R-value during their time in service, the manufacturing process for EPS creates a material that retains its thermal properties over time. An easy way to check insulation's predicted long-term performance is to read the warranty. EPS manufacturers typically offer a 20-year R-value warranty, while other leading insulation manufacturers' warranties acknowledge a potential R-value reduction within 10-15 years.
EPS is available in multiple compressive strengths. In some cases, insulation manufacturers have promoted products with higher compressive strengths than necessary for a given application. In many cases, you can use insulation with a lower compressive strength to save costs while still meeting a project's loading requirements. An important question to ask when selecting insulation is: "How much compressive resistance is really necessary?"
EPS has a low moisture absorption rate. According to tests by the U.S. Army's Cold Regions Research and Engineering Laboratory (CRREL), EPS buried in wetted soil for 1,000 days absorbed only 1.7 percent moisture by volume. In another demanding situation, EPS installed on a Minnesota testing laboratory's foundation and buried under soil was removed after 15 years and found to have only 5 percent moisture content compared with 19 percent moisture in another common foam insulation subjected to the same exposure on the same building.
The International Building Code (IBC) recognizes the use of EPS insulation in many roofing applications. You also can use EPS as part of an Underwriters Laboratories Inc. and FM Global fire-classified roof deck construction. Consult local codes and the insulation manufacturer for specific code requirements for a given roofing assembly, including the potential need for a thermal barrier separating EPS from a building's interior spaces.
EPS insulation types
EPS insulation is available in a wide array of products. In some cases, substituting EPS for other high-thermal resistance insulations will reduce labor and material costs.
EPS product options include:
There are some general guidelines for installing EPS insulation on various deck types and with assorted membranes. Consult insulation and membrane manufacturers' literature for specific requirements.
EPS insulation can be used with various steel deck types, including Type A (narrow rib), Type B (wide rib), Type F (intermediate rib) and Type N (deep rib). To ensure appropriate minimum thickness insulation, consult manufacturer's literature. You can use the material in direct-to-deck applications, but EPS insulation should be securely attached to the deck, typically with mechanical fasteners or adhesives.
As with any insulation, it is crucial to confirm a poured-in-place concrete deck is dry before installing EPS. Attaching EPS to concrete is frequently done by the "mop and flop" method with hot asphalt applied to the deck, allowed to cool below 250 F and the insulation placed over it. Urethane adhesives also are compatible and provide excellent uplift resistance.
EPS insulation also is compatible with plywood and OSB decks. Just as you would with other roof insulation, ensure a wood deck is dry and free of buckles, bulges or other surface irregularities before installing EPS insulation.
EPS insulation is well-suited for virtually all mechanically fastened single-ply roof systems, including thermosets (EPDM and CSPE) and thermoplastics (PVC, TPO, CPE and KEE). You can use EPS in ballasted and fully adhered single-ply systems, but remember to consult manufacturers' literature for insulation compatibility with membrane adhesives. Many petroleum-based and solvent-based adhesives can deteriorate EPS. In such cases, a suitable cover board—such as OSB, Securock® or DensDeck®—typically is required; composite EPS products that factory-bond these cover boards are an effective alternative.
Water- and urethane-based adhesives typically work well with EPS but may affect an assembly's fire rating (check local codes and the roof system component manufacturers' literature for details). In general, EPS products laminated with facers or composite EPS products that include factory-bonded cover boards can be used if EPS cannot be used directly under a membrane.
EPS insulation works effectively with conventional bituminous BUR membranes, but use of a cover board is required as are particular application techniques. Specifically, asphalt should only be applied to the substrate and not directly to the EPS. Asphalt should be adequately cooled (to between 200 F and 250 F) before EPS insulation is installed over it. Because of this narrow installation window, it is worthwhile to use an infrared heat gun and measure asphalt temperature before installing the first few EPS boards. EPS insulation board sizes should be limited to 4 feet by 4 feet when using this attachment method.
It is not acceptable to use coal tar with EPS insulation.
A good option
EPS insulation products are available for virtually any roofing need and can be customized to help speed installation and reduce the amounts of materials needed.
For additional information about EPS insulation roofing applications and installation tips, consult with an EPS insulation manufacturer. You also can visit the EPS Industry Alliance's website at www.epsindustry.org.
John Cambruzzi is director of sales and national accounts for Insulfoam, Tacoma, Wash.
EPS insulation substitutions for cost savings
With the multitude of EPS insulation products available, you can find one to meet the specific requirements of nearly any low- or steep-slope roofing job. In many cases, substituting EPS insulation for other high-thermal insulation can reduce labor and/or material costs. However, check with the roof system designer to verify a substitution is appropriate. Some ways to reduce costs by using EPS insulation include: